The complexity of modern integrated radio rooms creates a need to monitor and evaluate the operational readiness of equipment used in the transmission and reception of RF signals. Because one of the major objectives of the radio room is to configure various antennas and couplers to receivers and transmitters, it is of prime importance that the crosspoints of a configuration switching matrix be monitored for operability.
These antenna/transceiver configurations are changed on a periodic basis. The operator must know if the present configuration is maintaining antenna-receiver/transmitter crosspoint connectivity without performance degradation. He must also be aware of the operational readiness of other crosspoints so that future configurations can be made with confidence.
In order to ascertain the quality of an RF crosspoint within a matrix, a signal similar in characteristics to the actual receive or transmit signal must be passed through the crosspoint. This technique produces the highest confidence of crosspoint status. However, if a signal is passed through an antenna crosspoint which is actively configured, there is a risk that this quality check will exit the radio room via that configured antenna. In tactical situations, where the radio room operates in a covert environment, any surveillance monitoring by an enemy will detect this signal presence and reveal the radio room location. For this reason noise is a widely used signal source for operational readiness testing.
The use of noise as a signal source poses several advantages in checking RF crosspoints. The noise spectrum is easy to generate in the frequency range of crosspoint operation. In addition, if the noise does exit the radio room, it will be difficult to detect. In most instances the radiated noise will be below either the atmospheric or kelvin thermal noise floor at the surveillance receiver and be undetectable.
The generation of noise as a signal source, however, has several technical deficiencies. The output level of the noise varies from unit to unit of the same design. Therefore, if a crosspoint is to be monitored for degraded performance, such as increased insertion loss, a high percentage of false alarms or undetected failures will result, depending on how the detected level thresholds are set. Only a gross go/no go decision can be made with a high degree of confidence. Furthermore, degradation in frequency response of a crosspoint cannot be detected via noise injection techniques, since the noise power must be integrated over the entire band.